This article is mentioned in:

Abstract

Drug resistance remains a major challenge in epidermal growth factor receptor‑tyrosine kinase inhibitor (EGFR‑TKI) therapy. Bcl‑2‑like protein 11 (BIM), a B‑cell lymphoma 2 family pro‑apoptotic protein, is a prime target for specific anti‑cancer therapeutics. However, the epigenetic regulation of BIM in non‑small cell lung cancer (NSCLC) cell lines and patients with NSCLC in association with EGFR‑TKI resistance requires investigation. Methylation‑specific PCR (MSP), pyrosequencing, and nested quantitative (q)‑MSP were conducted to explore the methylation status of BIM in NSCLC cell lines. In addition, the methylation profile of BIM in patients with NSCLC was assessed by nested q‑MSP using circulating free DNA. Cell lines, treated with methylation inhibitor 5‑Aza‑2'‑deoxycytidine (AZA) or histone deacetylation inhibitor trichostatin A (TSA) prior to gefitinib treatment, were examined for BIM gene expression and resistance to gefitinib. All cell lines used in the present study presented with hypo‑methylated BIM. Treatment with AZA had no effect on BIM RNA expression in PC9 cells or the gefitinib‑resistant cell lines PC9/R and PC9/G2, nor did it reverse their resistance to gefitinib. In contrast, TSA treatment produced the opposite result. In the present study, 25 (78.1%) patients with hypo‑methylated BIM and 7 patients (21.9%) with partial or hyper‑methylated BIM were identified. The clinicopathological data revealed a random hypo‑methylated BIM distribution amongst patients with NSCLC. In the overall study group and EGFR mutant group, hypo‑methylated BIM carriers presented with no significant differences in progression free survival compared with patients with partial or hyper‑methylated BIM. All cell lines in the present study and the majority of patients with NSCLC carried hypo‑methylated BIM. Histone deacetylation, as opposed to promoter methylation, may contribute to the epigenetic silencing of BIM and lead to EGFR TKI resistance in NSCLC.